/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.support;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;

import org.springframework.context.ApplicationContext;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.http.server.reactive.HttpHandler;
import org.springframework.http.server.reactive.ServletHttpHandlerAdapter;
import org.springframework.util.Assert;
import org.springframework.web.WebApplicationInitializer;
import org.springframework.web.reactive.DispatcherHandler;
import org.springframework.web.server.WebHandler;
import org.springframework.web.server.adapter.HttpWebHandlerAdapter;

/**
 * Base class for {@link org.springframework.web.WebApplicationInitializer}
 * implementations that register a {@link DispatcherHandler} in the servlet
 * context, wrapping it in a {@link ServletHttpHandlerAdapter}.
 *
 * @author Arjen Poutsma
 * @since 5.0
 * @deprecated in favor of
 * {@link org.springframework.web.server.adapter.AbstractReactiveWebInitializer
 * AbstractReactiveWebInitializer}
 */
@Deprecated
public abstract class AbstractDispatcherHandlerInitializer implements WebApplicationInitializer {

    /**
     * The default servlet name. Can be customized by overriding {@link #getServletName}.
     */
    public static final String DEFAULT_SERVLET_NAME = "dispatcher-handler";

    /**
     * The default servlet mapping. Can be customized by overriding {@link #getServletMapping()}.
     */
    public static final String DEFAULT_SERVLET_MAPPING = "/";


    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        registerDispatcherHandler(servletContext);
    }

    /**
     * Register a {@link DispatcherHandler} against the given servlet context.
     * <p>This method will create a {@link DispatcherHandler}, initializing it with the application
     * context returned from {@link #createApplicationContext()}. The created handler will be
     * wrapped in a {@link ServletHttpHandlerAdapter} servlet with the name
     * returned by {@link #getServletName()}, mapping it to the pattern
     * returned from {@link #getServletMapping()}.
     * <p>Further customization can be achieved by overriding {@link
     * #customizeRegistration(ServletRegistration.Dynamic)} or
     * {@link #createDispatcherHandler(ApplicationContext)}.
     *
     * @param servletContext the context to register the servlet against
     */
    protected void registerDispatcherHandler(ServletContext servletContext) {
        String servletName = getServletName();
        Assert.hasLength(servletName, "getServletName() must not return empty or null");

        ApplicationContext applicationContext = createApplicationContext();
        Assert.notNull(applicationContext,
                "createApplicationContext() did not return an application " +
                        "context for servlet [" + servletName + "]");

        refreshApplicationContext(applicationContext);
        registerCloseListener(servletContext, applicationContext);

        WebHandler dispatcherHandler = createDispatcherHandler(applicationContext);
        Assert.notNull(dispatcherHandler,
                "createDispatcherHandler() did not return a WebHandler for servlet [" + servletName + "]");

        ServletHttpHandlerAdapter handlerAdapter = createHandlerAdapter(dispatcherHandler);
        Assert.notNull(handlerAdapter,
                "createHttpHandler() did not return a ServletHttpHandlerAdapter for servlet [" + servletName + "]");

        ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, handlerAdapter);
        Assert.notNull(registration,
                "Failed to register servlet with name '" + servletName + "'." +
                        "Check if there is another servlet registered under the same name.");

        registration.setLoadOnStartup(1);
        registration.addMapping(getServletMapping());
        registration.setAsyncSupported(true);

        customizeRegistration(registration);
    }

    /**
     * Return the name under which the {@link ServletHttpHandlerAdapter} will be registered.
     * Defaults to {@link #DEFAULT_SERVLET_NAME}.
     *
     * @see #registerDispatcherHandler(ServletContext)
     */
    protected String getServletName() {
        return DEFAULT_SERVLET_NAME;
    }

    /**
     * Create an application context to be provided to the {@code DispatcherHandler}.
     * <p>The returned context is delegated to Spring's
     * {@link DispatcherHandler#DispatcherHandler(ApplicationContext)}. As such,
     * it typically contains controllers, view resolvers, and other web-related beans.
     *
     * @see #registerDispatcherHandler(ServletContext)
     */
    protected abstract ApplicationContext createApplicationContext();

    /**
     * Refresh the given application context, if necessary.
     */
    protected void refreshApplicationContext(ApplicationContext context) {
        if (context instanceof ConfigurableApplicationContext) {
            ConfigurableApplicationContext cac = (ConfigurableApplicationContext) context;
            if (!cac.isActive()) {
                cac.refresh();
            }
        }
    }

    /**
     * Create a {@link DispatcherHandler} (or other kind of {@link WebHandler}-derived
     * dispatcher) with the specified {@link ApplicationContext}.
     */
    protected WebHandler createDispatcherHandler(ApplicationContext applicationContext) {
        return new DispatcherHandler(applicationContext);
    }

    /**
     * Create a {@link ServletHttpHandlerAdapter}.
     * <p>Default implementation returns a {@code ServletHttpHandlerAdapter} with the provided
     * {@code webHandler}.
     */
    protected ServletHttpHandlerAdapter createHandlerAdapter(WebHandler webHandler) {
        HttpHandler httpHandler = new HttpWebHandlerAdapter(webHandler);
        return new ServletHttpHandlerAdapter(httpHandler);
    }

    /**
     * Specify the servlet mapping for the {@code ServletHttpHandlerAdapter}.
     * <p>Default implementation returns {@code /}.
     *
     * @see #registerDispatcherHandler(ServletContext)
     */
    protected String getServletMapping() {
        return DEFAULT_SERVLET_MAPPING;
    }

    /**
     * Optionally perform further registration customization once
     * {@link #registerDispatcherHandler(ServletContext)} has completed.
     *
     * @param registration the {@code ServletHttpHandlerAdapter} registration to be customized
     * @see #registerDispatcherHandler(ServletContext)
     */
    protected void customizeRegistration(ServletRegistration.Dynamic registration) {
    }

    /**
     * Register a {@link ServletContextListener} that closes the given application context
     * when the servlet context is destroyed.
     *
     * @param servletContext the servlet context to listen to
     * @param applicationContext the application context that is to be closed when
     * {@code servletContext} is destroyed
     */
    protected void registerCloseListener(ServletContext servletContext, ApplicationContext applicationContext) {
        if (applicationContext instanceof ConfigurableApplicationContext) {
            ConfigurableApplicationContext context = (ConfigurableApplicationContext) applicationContext;
            ServletContextDestroyedListener listener = new ServletContextDestroyedListener(context);
            servletContext.addListener(listener);
        }
    }


    private static class ServletContextDestroyedListener implements ServletContextListener {

        private final ConfigurableApplicationContext applicationContext;

        public ServletContextDestroyedListener(ConfigurableApplicationContext applicationContext) {
            this.applicationContext = applicationContext;
        }

        @Override
        public void contextInitialized(ServletContextEvent sce) {
        }

        @Override
        public void contextDestroyed(ServletContextEvent sce) {
            this.applicationContext.close();
        }
    }

}
